A sound wave propagating through a gas or fluid and an elastic wave propagating through a solid medium are collectively called an “acoustic wave”.
Acoustic sensors for receiving a sound wave or an ultrasonic wave and generating an electric signal corresponding to vibration of the wave may be classified into a microphone, a subaqueous sound hydrophone (i.e., a subaqueous sound locator), an ultrasonic wave sensor, a sound emitting sensor, and the like, depending on a frequency band to be measured, a medium, and an object to be measured.
Also, acoustic sensors may be generally classified into resonant acoustic sensors and broadband acoustic sensors depending on measurable frequency bandwidths.
The resonant acoustic sensors have good signal reception sensibility and a high signal-to-noise ratio (SNR) but a narrow measurable frequency band. The broadband acoustic sensors have a relatively wider measurement frequency band but bad reception sensibility and a low signal-to-noise ratio.